Mercury arc rectifier



Nov. 12, 1935. J. SLEPIAN EI'AL MERCURY ARC RECTIFIER Filed NOV. 25,1932 2 Sheets5heet l I III lllll INVENTORS- Jase ab 5/0/40 [em RLudW/y.

ewwzm ATTORNEY Nov. 12, 1935. J. SLEPIAN ETAL 2,020,915

MERCURY ARC RECTIFIER Filed Nov. 25, 1932 2 Sheets-Sheet 2 JW 5%) I I WATTORNEY Patented Nov. 12,,1935

UNITED STATES LIERCURY ARC RECTIFIER Joseph Slepian, Pittsburgh, andLeon B. Ludwig, burg, Pa., assignors to Westinghouse Electric &Manufacturing Company,

East

Pittsburgh, Pa., a corporation of Pennsylvania Application November 25,1932, Serial No. 644,212

9Claims.

Our invention relates to vapor electric devices and particularly tomake-alive circuits for such devices.

In our copending application Serial No. 626,866, we have disclosed avapor electric device having a make-alive for establishing a cathodespot at the beginning of each active period in the rectifier.

In the operation of vapor electric devices having make-alives,considerable difficulty has been experienced in initiating the cathodespot. According to our invention, the cathode spot is initiated by meansof a discharge initiated by the voltage in the anode circuit.

It is an object of our invention to provide a make-alive device which issubstantially independent of the fluctuations of the cathode surface andin which the make-alive electrode is substantially separated from thecathode.

It is a further object of our invention to provide an intensifiedcathode spot initiating dis-'- charge initiated from the anode circuit.

Other objects and advantages of our invention will be apparent from thefollowing detailed description taken in conjunction with theaccompanying drawings, in which:

Figure 1 is a schematic illustration of a rectifier embodying ourinvention.

Fig. 2 is a modification showing the use of fioating bodies forassisting in the cathode spot formation.

Fig. 3 is a similar illustration showing a highly cooled cathode foraiding the cathode spot formation.

Fig. 4 is a similar view of a further modification, and

Fig. 5 is amodification showing further means of initiating the cathodespot.

It has frequently been proposed to start an arc with cathode on themercury pool of a mercury arc vessel, by means of a. discharge from anauxiliary electrode, this discharge being initiated by the applicationof sufllciently high voltage to the auxiliary electrode. It is usuallyoverlooked however that such a discharge initiated in this way,generally takes the form of a glow, without the formation of an arccathode spot on the mercury pool. While it is true that a glow to amercury pool cathode has a certain degree of instability,

and that under its influence, a cathode spot may form spontaneously,nevertheless, it is our experience that such spontaneous formation ofcathode spots are erratic and random in their occurrence, and do notoccur with sufficient frequency to serve for the purposes of thisinvention without the; use of devices described herein for greatlyincreasing the probability of occurrence of the cathode spots. Withoutthe use of such devices and means, cathodes of an arc may be struck tothe mercury pool occasionally, but not regularly cycle after cycle as iscontemplated in this invention.

We have found that the probability of formation of a cathode spot from aglow type of discharge to a mercury pool is greatly increased by 1increasing the intensity of the discharge, and we have devised means forso increasing the intensity at local points on the mercury surface as tomake certain that a cathode spot will be formed with negligible timedelay. 15

In the modification according to Fig. 1 the vapor electric devicecomprises a mercury cathode I insulated by a suitable insulator 2 from aclosely spaced anode 3. Insulated from both the anode 3 and the cathodel is an auxiliary electrode or 20 make-alive comprising a thermionicelement 5 adapted to be connected to the cathode through a suitabletransformer. While any suitable transformer may be used, it ispreferable to use a special device such as a Tesla transformer 1 capable25 of producing not only a-high potential but a high frequency as well.We have found that if an auxiliary high frequency discharge isinaugurated between an established cathode and the mercury, theprobability of back-fire is so high when the 30 high frequency polarityreverses that a cathode spot will be formed with certainty on themercury pool. Located between the anode and the transformer is asuitable unidirectional conductor or rectifier 8 for transmittingcurrent to the pri- 35 mary of the transformer I only when properpotential is applied to the anode 3 as by the transformer 9. Preferablythe auxiliary electrode is substantially enclosed in a. suitable shieldl2.

In the operation of our device, the thermionic 40 cathode 5 is normallyinsulated from the vaporizable electrode. Upon the application of properpotential to the anode, by the transformer 9, the auxiliary rectifier 8carries current and energizes the make-alive transformer I which causesconduction of current between the vaporizable electrode l and theauxiliary thermionic cathode 5. The high frequency current impressedbetween the auxiliary cathode 5 and the vaporizable cathode I reversesso rapidly that the current path between the auxiliary electrode and thevaporizable electrode remains ionized while the high frequency potentialpasses through zero and builds up a positive potential on the auxiliaryelectrode. This positive potential between the auxiliary electrode andthe mercury pool together with the momentary high positive ion currentto the mercury pool causes current to flow to the mercury pool andestablishes a cathode spot thereon. The main rectifying arc establishesitself to this cathode spot and effectively short circuits the auxiliaryrectifier I and the makealive transformer I so that the make-alive arcis extinguished and only the current carrying arc remains in the device.

In themodification shown in Fig. 2, the thermionic auxiliary cathode 5is replaced by a plain electrode. We have found that when certain bodiesare floated on a mercury surface, in the presence of a glow or otherback current discharge, the probability of the formation of a cathodespot is made very high. This may be explained as due to small patches onthe float- 'ing bodies which become charged in the presence of the glowcurrent, and later break down", yielding the arc cathode. Carborundum,quartz, glass, and various resistance materials are examples of the typeof material used for the floating bodies. On the surface of thevaporizable cathode adjacent to the auxiliary cathode, we have placed acoating of resistance material such as carborundum H, a suitable barrieris provided for retaining the resistance material in the desiredlocation. The barrier may be in the form of a water cooled coilsubmerged just below the mercury surface. It is desirable that thisbarrier should be coated with a refractory metal such as tungsten ormolybdenum. In the operation of our device, according to thismodification, the auxiliary rectifier 8 conducts upon the application ofthe proper polarity of potential to the anode 3 and energizes theprimary of a suitable transformer 20. The secondary of the transformer20 is then energized to impress a potential between the auxiliaryelectrode I5 and the vaporizable electrode The high potential causes adischarge probably in the form of a glow discharge between the auxiliaryelectrode and the vaporizable electrode. The presence of the highresistance material on the surface of the vaporizable electrode causesthe glow discharge to concentrate and establish a cathode spot on thevaporizable electrode I. If desired, a suitable condenser 2| may beplaced across the secondary terminals of the transformer 20. Thiscondenser, upon the formation of a glow discharge, will be discharged inparallel with the transformer secondary and materially increase thecurrent density in the discharge and materially assist in the formationof a cathode spot.

In the modification shown in Fig. 3, a suitable high frequency generator25 has been inserted between the transformer 20 and the auxiliaryelectrode. Instead of using high resistance material on the vaporizableelectrode, we prefer to strongly cool a portion 26 of the electrodeadjacent to the auxiliary electrode. Cold bodies in a vacuum device, inparticular cold mercury, we believe are usually contaminated by patchesof relatively high dielectric strength on their surfaces. We have foundthat on the surface of cold mercury for example, oxides, nitrides, etc.are present, and that in the presence of a glow discharge, such patchesbecome charged and later break down yielding a cathode spot. In anycase, regardless of the theory, we have found that cold mercury readilyforms an arc cathode under the influence of a glow or positive ioncurrent arising from any source. Upon the application of suitablepotential to the anode 3, the auxiliary rectifier I permits current flowthrough transformer 20 the secondary of which discharges through thehigh frequency generator and produces a high frequency discharge betweenthe auxiliary electrode II and the vaporizable eleca trode i. Thepresence of the strongly cooled portion 26 of the vaporizable electrode,probably by inducing the formation of mercury oxides or nitrides at themercury surface, causes a concentration of the glow discharge and aconse- 1o quent formation of a cathode spot. Obviously, the transformerand high-frequency generator could be replaced by a Tesla transformerwhere the relatively low frequency of the Tesla transformer interrupteris sufficiently high to cause II the formation of a cathode spot asoften as is desired.

In the modification shown in Fig. 4, the auxiliary cathode is in theform of a thermionic cathode 30 which is connected to the vaporizable l0electrode by a suitable resistance 3|. The shield i2 surrounding theauxiliary electrode 30 extends within very closely spaced relation withthe vaporizable electrode Upon the anode 1 being energized with theproper potential, a ll discharge will take place between the anode andthe auxiliary electrode 30. Thisv discharge will pass through therestricted space 33 between the shield l2 and the vaporizable electrodeI, in effect pinching the are against the surface of 80 the vaporizableelectrode. The resistance 3| between the auxiliary electrode and thevaporizable cathode causes a difference of potential between the arc andthe surface of the vaporizable electrode adjacent to the arc. Because ofthe crowding of the arc next to the mercury surface, a very high densityof ionization exists there, and under the influence of this differenceof potential, a large positive ion current flows to the mercury whichcauses a current'to flow to the vaporizable 4o electrode and establishesa cathode spot thereon to which the current rectifying are immediatelyattaches and short circuits the resistance 3| between the auxiliaryelectrode and the vaporizable electrode. 5

In the modification according to Fig. 5, the auxiliary electrode is inthe form of a tubular member 35 dipping into the mercury electrode andhaving at least a portion 36 adjacent to the mercury electrode ofinsulating material such as 50 quartz. A suitable nozzle 31 extends fromthe electrode and terminates in closely spaced relationship with thevaporizable electrode I. A heating element 38 supplied from a suitablepower source 39 is connected in spaced relationship in 6|} saidauxiliary electrode.

We have found that the probability of the formation of a cathode spotfrom a glow type of discharge is greatly increased by increasing thepressure of the gas at the region near the cathode. N This is probablybecause the current density at the cathode of a glow varies as thesquare of the density of the gas in which the glow is playing.Consequently, we have devised means for causing high local vaporpressures of the mercury which 05 will be sufllcient so that a glowformed by the application of sufficient voltage will certainly change toan arc with negligible time delay.

In operation, the heating element 18 is supplied with current to producea high vapor pres- 70 sure in the auxiliary electrode 35 which isdischarged through the nozzle 31 and against the mercury surface. whenproper potential is applied to the anode 3 the transformer 20 isenergized and a discharge takes place between the 7 nozzle 81' and themercury surface. The high vapor density in the vicinity of the nozzlecauses a highly concentrated discharge which results in the formation ofa cathode spot on the mercury surface. I

While we have shown and described specific embodiments of our invention,it is apparent that changes and modifications can be made thereinwithout departing from the spirit and scope of our invention. We desire,therefore, that only such limitations shall be imposed as are embodiedin the accompanying claims or as may be necessitated by the prior art.

We claim as our invention:

1. A vapor electric device comprising an anode, a cathode, an auxiliaryelectrode spaced from both the anode and cathode, a transformer having aprimary and secondary winding, the primary being connected between theanode and cathode,

means in series with the transformer primary for permitting current flowin the primary only during the prevalence of a predetermined polarity ofpotential between said anode and said cathode, the secondary beingconnected between the cathode and the auxiliary electrode.

2. In a vapor electric device comprising an anode and a cathode, amake-alive comprising an auxiliary thermionic cathode, a shield aboutthe thermionic cathode, a source of high frequency current havingterminals connected to said thermionic cathode and the main cathode andmeans connected to the anode for actuating the source of high frequencycurrent.

3. An electrical translating device comprising a container, a maincathode and an anode in said tainer, said electrode being spaced fromthe main cathode and anode, an alternating current system connected tosaid anode, a direct current system connected to said cathode, anexternal circuit between said cathode and said anode, an externalcircuit between said cathode and said auxiliary rent carrying arebetween said anode and cathode for each conducting half cycle.-

4. An electrical device comprising a container, a main cathode and anodein said container, an electrode in said, container,

3 circuit between said cathode and said auxiliary electrode, a highfrequency transformer connected between said external circuits forinitiating a current carrying are between said anode and cathode, andvalve means in said first mena timed circuit for controlling said' highfrequency transformer in response to the polarity of the anodepotential.

5. In a vapor electric device having a main cathode and an anode, anauxiliary thermionic 1o cathode, a high frequency generator connected tosaid main cathode and to said auxiliary cathode, and a unidirectionalconductor connected between the anode and the high frequency generatorfor actuating the generator only when potential of a predeterminedpolarity is applied to the anode.

6. In a vapor electric device having a main cathode and an anode, anauxiliary thermionic cathode, a high frequency gene'rator connected tosaid main cathode and to said auxiliary cathode, means for supplyingcurrent to the high frequency generator and a unidirectional conductorfor controlling the fiow of current to the high frequency generator.

7. A vapor-electric device comprising an evacuated container, 9.vaporizing cathode therein, an anode closely spaced from said cathode,an auxiliary electrode in said container, means for creating a highvapor pressure in the vicinity of said auxiliary electrode and means forsupplying potential to said auxiliary electrode only when said anode ispositive with respect to said anode.

8. A vapor electric device comprising a chamber, an anode and a cathodein spaced relation in said chamber, an auxiliary electrode spaced fromsaid anode and said cathode and means for applying potential to saidauxiliary electrode for initiating an electrical discharge between saidauxiliary electrode and said cathode and means 40. for causing theformation of a cathode spot on said cathode said means consisting ofmeans for producing a high vapor density at some local point of thecathode surf 9. Avapor electric converter comprising a pair as of mainelectrodes, an ignition transformer the primary of which is connectedacross said main electrodes, an auxiliary electrode in said con- LION n.'wnwm: is

